1. Field of the Invention
Concern for environmental safety requires the need to find methods in which to more effectively dispose of hazardous waste. This invention relates to a method for the enhanced biological remediation of chlorinated hydrocarbon pollutants. This is accomplished by inoculation of a contaminated substrate with a novel strain of Actinomyces viscosus.
2. Description of the Prior Art
Conventional techniques for remediation of toxic waste sites have focused on approaches utilizing excavation, filtration or immobilization. These techniques often do not include the transformation of the contaminants into innocuous products, but serve only to contain and/or concentrate the hazardous materials. By contrast, bioremediation techniques offer the potential to convert toxic contaminants into end products that are either less toxic or non-toxic. Bioremediation is hence developing as the method of choice over conventional remediation methods.
The U.S. Environmental Protection Agency (EPA) has invested heavily in research to develop bioremediation schemes for numerous toxic and mutagenic chemicals including chlorinated aromatic compounds. Homocyclic aryl chlorides, due to chlorination of the aromatic ring, are of low solubility and are thus recalcitrant to natural biodegradation. Research emphasis has consequently been placed on bioremediation schemes that dechlorinate the aromatic ring, thereby increasing compound solubility and exposure to microbiological degradation.
Pentachlorophenol (PCP) is a toxic and mutagenic chlorinated aromatic compound that is still routinely used as a biocide for wood preservation in the United States. Outside the U.S. PCP use is even more widespread. Consequently, the U.S. EPA has classified PCP as a priority pollutant. Numerous bacteria have been isolated in culture that can biodegrade PCP and other chlorinated aromatic compounds under aerobic conditions, however, attempts to biodegrade PCP under anaerobic conditions, which prevail at toxic waste sites, can result in either no PCP removal (Mohn et al., Appl. Environ. Microbiol., 1992, 58, pp. 1367-1370) or generation of pentachloroanisole as the main product (Kuhn et al., Soil Sci. Soc. America; 1989, 22, pp. 111-180; Lamar et al., Appl. Environ. Microbiol., 1990, 56, pp. 3093-3100). Although pentachloroanisole is less toxic than PCP, it is more stable and thus less amenable to further biodegradation.
PCP biodegradation under anaerobic conditions proceeds predominantly by the mechanism of reductive dechlorination as the initial step. Reductive dechlorination involves a two electron transfer in which chlorine is removed as chloride (Cl-) from homocyclic aryl chlorides and replaced by a proton (H+) from water. Reductive dechlorination of chlorinated aromatic compounds by microbial consortia have been studied in sludges and sediments under methanogenic-type, anaerobic conditions (Bryant et al., Appl. Environ. Microbiol., 1991, 57, pp. 2293-2301), however, a period of adaptation to the presence of chlorophenols is often required to establish effective rates of dechlorination Nicholson et al. (Appl. Environ. Microbiol., 1992, 58, pp. 2280-2286) have published a summary of pathways of reductive dechlorination of chlorophenols by non-adapted and adapted microbial consortia.
One anaerobic bacterium isolated in pure culture, Desulfomonile tiedjei (DCB-1), removes chlorine and derives energy and carbon from 4-chlorobenzoic acid. Reductive dechlorination of 4-chlorobenzoic acid proceeds by reduction of the aromatic ring and the addition of a proton derived from water. DCB-1 also dechlorinates PCP at low concentrations (&lt;3 .mu.g/ml) but only as a detoxifying mechanism since neither energy or carbon is derived from PCP (Mohn et al., Appl. Environ. Microbiol., 1992, 58, pp. 1367-1370). Desulfomonile tiedjei, taxonomically is a sulfate-reducer and the reduction of sulfate is preferred over dechlorination as a means of removing reducing equivalents (DeWeerd et al., Appl. Environ. Microbiol., 1991, 57, pp. 1929-1934).